Adding Other types of Custom Properties
AFAIK you can set up all but boolean by using that type in the property value field.  Eg type in integer 1 and you will notice the slider moves by integers, even if min and max are displayed as reals.

For vector floats, typing in (1.0, 0.0, 0.0, 0.0) gives a list usable for rgba values.

&gt;&gt;&gt; C.scene['prop']
&lt;bpy id property array [4]&gt;

&gt;&gt;&gt; C.object.color = C.scene['prop']

&gt;&gt;&gt; [c for c in C.scene['prop']]
[1.0, 0.0, 0.0, 1.0]


To define them with a script is pretty simple too

import bpy
context = bpy.context
scene = context.scene
scene["someprop"] = False


To get a little more into it, the _RNA_UI is where custom properties keep their data, min, max, default, description

import bpy

context = bpy.context
obj = context.object

rna_ui = obj.get('_RNA_UI')
if rna_ui is None:
    obj['_RNA_UI'] = {}
    rna_ui = obj['_RNA_UI']

obj["prop"] = (1.0, 0.0, 0.0, 1.0)
obj["bool"] = 0

rna_ui["bool"] = {"description":"Bool",
                  "default": True,
                  "min":0,
                  "max":1,
                  "soft_min":0,
                  "soft_max":1}

rna_ui["prop"] = {"description": "Color Prop",
                  "default": (1.0, 0.0, 0.0, 0.0),
                  "min": 0.0,
                  "max": 1.0,
                  "soft_min":0.0,
                  "soft_max":1.0,
                  }


You can add these to your own layout

import bpy
from bpy.props import FloatVectorProperty, BoolProperty

class CarPanel(bpy.types.Panel):
    """Creates a Panel in the Object properties window"""
    bl_label = "Car Details"
    bl_idname = "OBJECT_PT_hello"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "object"

    @classmethod
    def poll(cls, context):
        return context.object.get("Capot", False)

    def draw(self, context):
        layout = self.layout

        car = context.object
        layout.prop(car, '["Capot"]')
        #bools don't show well (1 or 0 integer)
        layout.prop(car, "switch")
        layout.prop(car, '["bool"]')
        col = layout.column()
        col.prop(car, '["prop"]')
        # car color property
        row = layout.row()
        row.prop(car, "car_color")
        # object color rgba
        row = layout.row()
        row.prop(car, "color")

def register():
    # define a registered property (available for all Object types size=4 gives rgba)
    bpy.types.Object.car_color = FloatVectorProperty(subtype='COLOR', size=3)
    bpy.types.Object.switch = BoolProperty()
    bpy.utils.register_class(CarPanel)

def unregister():
    bpy.utils.unregister_class(CarPanel)

if __name__ == "__main__":
    register()